The present invention relates in general to pressure transducers and is concerned, more particularly, with a new and improved fluid-filled, direct sensing pressure transducer, the principles of which are particularly adapted for pressure sensing associated with an injection molding machine. The transducer of the present invention is characterized by a high cycle life and miniaturized size so as to permit cavity pressure measurements directly at the mold.
U.S. Pat. Nos. 3,349,623; 3,678,753, owned by the assignee herein, show fluid-filled pressure transducers. The transducers described in these patents, although useable in measuring pressures associated with various types of molding operations, are not readily adaptable as a pressure transducer for injection molding machines.
Accordingly, the primary object of the present invention is to provide a fluid-filled pressure transducer that is adapted for use with injection molding equipment. In comparison with the transducers described in the aforesaid patents, the transducer of this invention is of miniaturized size and designed to be mounted inside a mold to measure cavity pressure directly associated with an injection molding process.
A further object of the present invention is to provide an improved injection molding pressure transducer that is characterized by substantial fatigue resistance, thus, enabling high cycle life.
Still another object of the present invention is to provide an improved pressure transducer that is fluid filled and that has an improved sensing technique preferably employing a thick-walled cylinder configuration that minimizes overall working stress.
Another object of the present invention is to provide an improved fluid-filled pressure transducer that employs a filler rod for reducing the internal volume, thereby replacing the capillary arrangement as shown in the aforesaid patents. This replacement means a substantial ease in manufacture of the transducer. Furthermore, the use of a filler rod may be adopted as a vibration damper against resonances induced through transient pressure excitations.
Still a further object of the present invention is to provide an improved fluid-filled pressure transducer employing a minimum volume of fluid for reduced temperature effects.
Another object of the present invention is to provide an improved fluid-filled pressure transducer, preferably adapted for use with injection molding equipment and which is further characterized by an improved fill and seal mechanism. The transducer is preferably sealed under 100 p.s.i. line pressure applied through a hollow break-away fill screw which precharges the transducer and internally to 100 p.s.i. The filling technique also prestresses the coupling diaphragm, thus, reducing peak working tensile stresses by one the order of one half to significantly improve fatigue life of the transducer.